Plasma display panels (PDPs) are a type of plasma display devices. PDPs enable large-screen slimline displays to be produced relatively easily, and so are receiving attention as the coming generation of display panels. Sixty-inch models have already been commercialized.
FIG. 5 is a partially sectional and perspective view showing a main construction of a typical surface discharge AC (alternating current) PDP. In the drawing, the direction z represents the direction along the thickness of the PDP, and the plane xy represents a plane which is parallel with the panel plane of the PDP. As illustrated, the PDP 2 is roughly made up of a front panel 20 and a back panel 26 which are arranged with their major surfaces facing each other.
A front panel glass 21 is a substrate of the front panel 20. A pair of display electrodes 22 and 23 (an X electrode 22 and a Y electrode 23) are formed on one of the major surfaces of the front panel glass 21 so that each electrode runs along the direction x. Surface discharge is performed between these electrodes. The display electrodes 22 and 23 are formed by placing bus lines 221 and 231 made of a mixture of Ag and glass, on top of transparent electrodes 220 and 230 formed from ITO (Indium Tin Oxide) and the like.
A dielectric layer 24 made of a dielectric material is formed at the center of the major surface of the front panel glass 21 on which the display electrodes 22 and 23 have been arranged. A protective layer 25 having the same size as the dielectric layer 24 is formed on the dielectric layer 24.
A back panel glass 27 is a substrate of the back panel 26. A plurality of address electrodes 28 are formed in stripes on one of the major surfaces of the back panel glass 27 with a predetermined spacing, so that each electrode runs along the direction y. The address electrodes 28 are formed from a mixture of Ag and glass, like the bus lines 221 and 231. A dielectric layer 29 made of a dielectric material is formed at the center of the major surface of the back panel glass 27 so as to cover the address electrodes 28. Barrier ribs 30 are arranged on the dielectric layer 29 at the gaps between the adjacent address electrodes 28. Phosphor layers 31-33 corresponding to the colors of red (R), green (G), and blue (B) are applied to the side faces of the adjacent barrier ribs 30 and the surface of the dielectric layer 29 between the adjacent barrier ribs 30.
Such constructed front panel 20 and back panel 26 are positioned so that the address electrodes 28 cross over the display electrodes 22 and 23 at right angles. The front panel 20 and the back panel 26 are then sealed at their edges to make the inside airtight. In more detail, frit glass as a sealing member 40 is applied to the edges of the front panel glass 21 (more precisely, around the dielectric layer 24) and the edges of the back panel glass 27 (more precisely, around the dielectric layer 29), as shown in a top view of FIG. 6. This sealing member 40 is melted to seal the panels 20 and 26. Here, the edges 211 and 212 of the front panel glass 21 and the edges 271 and 272 of the back panel glass 27 are outlets for respectively connecting the display electrodes 22 and 23 and the address electrodes 28 to outside drive circuits (not illustrated).
Note that in FIG. 6 the number of display electrodes 22 and 23 and the number of address electrodes 28 are fewer than in actual PDPs for purposes of illustration. The electrodes are indicated by solid lines. Also, the positions of the sealing member 40 and dielectric layer 24 are indicated by solid lines.
A discharge gas (an enclosed gas) including Xe is introduced between the front panel 20 and the back panel 26 which are sealed together, at a predetermined pressure (typically about 40 kPa-66.5 kPa).
As a result, the spaces which are separated by the dielectric layer 24, the phosphor layers 31-33, and the adjacent barrier ribs 30 between the front panel 20 and the back panel 26 become discharge spaces 38. Also, the areas at which the pairs of adjacent display electrodes 22 and 23 cross over the address electrodes 28 with the discharge spaces 38 in between become cells for image display (not illustrated).
To drive the PDP, discharge is started between the address electrode 28 and the display electrode 22 or 23 in each cell. Then ultraviolet light of short wavelength (Xe resonance lines with a wavelength of about 147 nm) is generated from glow discharge between the pair of display electrodes 22 and 23, and excites the phosphor layers 31-33 to emit light. This produces an image display.
The above constructed PDP, however, has the following problem.
FIG. 7 is a sectional view of an edge part of the PDP and its vicinity (taken along an address electrode 28). The sealing member 40 made of frit glass is melted and fixed between the back panel glass 27 and the dielectric layer 24, and also melted and fixed between the address electrode 28 and the dielectric layer 24 as shown in the drawing. When melting the sealing member 40 between the address electrode 28 and the dielectric layer 24, the address electrode 28 is heated together with the sealing member 40, which causes Ag particles in the address electrode 28 to diffuse and seep into the sealing member 40.
This diffusion of Ag particles cause the address electrode 28 to partially break and its conductivity to drop. This may even result in shortening of a plurality of address electrodes 28. Moreover, the seepage of Ag particles in the sealing member 40 degrades the sealing member 40 and reduces its sealing performance.
The same problem may occur between the sealing member 40 and the display electrode 22 (23). FIG. 8 is a sectional view showing an edge part of the PDP and its vicinity (taken along a bus line 221 (231)). The drawing shows the state where Ag particles in the bus line 221 has seeped into the sealing member 40. This causes the bus line 221 (231) of the display electrode 22 (23) to short out or break, resulting in a decrease in performance of the PDP.
This problem is especially evident with PDPs that have a fine cell structure such as those for use in high-definition television, i.e., PDPs that have very narrow bus lines and address electrodes. An immediate solution is required.